Field of the Invention--This invention concerns water-cooled, workpiece-supporting members for use in heating furnaces for steel workpieces and, more particularly, to improved riders and buttons for use in pusher furnaces, in walking beam furnaces, and in composite furnaces.
Description of the Prior Art--Reheat furnaces for steel workpieces are typically pusher furnaces (U.S. Pat. Nos. 3,148,868; 4,540,364; 4,427,371), walking beam furnaces (U.S. Pat. Nos. 3,749,550; 4,290,752), or, composite furnaces (U.S. patent application Ser. No. 874,393 filed Apr. 27, 1992). Each of these furnaces provides a series of lengthwise supports, frequently called skids, with workpiece-supporting members secured to the top thereof for supporting steel workpiece in their movement through the reheat furnace. The workpieces are usually steel slabs 9 to 10 inches thick, 30 to 82 inches wide and 30 to 40 feet long. The workpieces are heated from ambient temperatures to final temperatures of 2100.degree. to 2500.degree. F. depending upon the steel and the intended use of the steel.
Pusher Furnaces--The workpiece supporting members in pusher furnaces are called riders and are secured to the top of lengthwise support members, frequently hollow conduits containing water for the purpose of cooling the skid and cooling the rider (U.S. Pat. Nos. 4,354,824; 4,601,659). Workpieces are abutted front-to-back in the pusher furnace and are advanced through the pusher furnace supporting on the riders. As a fresh steel workpiece is introduced into the charging end of a pusher furnace, a corresponding heated steel workpiece is extracted from the discharge end of the furnace for rolling mill treatments or other processing. Riders typically are 3 to 5 inches high.
Walking Beam Furnaces--A typical walking beam furnace has multiple horizontal lengthwise skids which are securely fixed with respect to the furnace and has intermediate lengthwise horizontal skids (the walking skids) which are equipped to rise upwardly, advance forwardly, withdraw downwardly and return to the original position. The fixed skids and the walking skids are equipped with spaced-apart buttons which are secured to the skid and extend vertically upwardly to support and engage steel workpieces throughout the length of the furnace (U.S. Pat. Nos. 4,609,347; 4,906,525). Relatively tall buttons greater than 120 mm have been proposed (U.S. Pat. No. 4,747,775). The fixed skids and walking skids are frequently hollow pipes through which water flows to maintain a low temperature for the skids and the buttons (U.S. Pat. Nos. 4,687,027; 4,293,299; 4,591,340).
Composite Furnace--A composite steel workpiece reheat furnace is described in co-pending patent application Ser. No. 874,393 filed Apr. 27, 1992 by Frank Campbell and Hugh J. Harding. The composite furnace is a pusher furnace adjacent the charging end and becomes a walking beam furnace adjacent the discharge end. The composite furnace employs riders to support steel workpieces in the pusher portion and employs buttons secured to the fixed skids and walking skids in the walking beam portion of the reheat furnace.
Skid Marks--A serious concern of steel manufacturers is the consequence of skid marks on steel workpieces which are produced in steel reheat furnaces (U.S. Pat. Nos. 5,007,824; 4,884,967; 4,936,771). Skid marks result from two principal phenomena:
1. The riders or buttons are maintained at a lower temperature than the design temperature for discharging steel workpieces. As a consequence, there is a transfer of heat from each steel workpiece conductively into the riders and buttons through the bottom, supported surface of the steel workpieces which are in contact with the top surfaces of the riders and buttons. The resulting temperature along the line of the skids is lower adjacent to the bottom surface of the steel workpiece than the workpiece temperatures throughout the body of the steel workpiece. These regions of lowered temperatures are called "skid marks" and result in differential metallurgical properties of the steel workpiece. PA0 2. In a steel reheat furnace, radiant heat energy is directed into the steel workpiece from radiant fuel burners which may be above the steel workpieces and which may be below the steel workpieces, or both. In addition, the interior walls, ceiling and floor of the steel reheat furnaces are radiating surfaces directing and re-directing radiant heat energy toward the steel workpieces. In the regions of the buttons and riders where the straight line access of radiant energy to the undersurface of the steel workpieces is shielded by skids, buttons, riders or any other structure (e.g., cross braces connecting skids). The heat delivery to the under surface of the steel workpieces is greater between adjoining skids than at the regions above any skid. Accordingly a cooler bottom surface is presented along the line of the skids as a result of the significant shadow effect of the skids and the riders or buttons. This shadow effect coincides with the thermal conduction from the workpiece through the riders or buttons and creates regions of lower temperatures which are the "skid marks".
Numerous solutions have been proposed to reduce the skid marking tendencies of steel reheat furnaces to produce a heated steel workpiece having a generally uniform temperature profile across its bottom surface corresponding to the generally uniform temperature profile across the top of the steel workpiece. As the steel market demands increasing uniformity in sheet steel products, the steel industry is becoming more concerned about eliminating or significantly reducing the skid mark phenomenon (U.S. Pat. Nos. 5,007,824; 4,936,771; 4,884,967).